Araucaria fans will do the crossword anywhere, any time – in the middle of a bungee jump if necessary – but we do have our favourite spots. Mine would be in front of a crackling wood fire in the middle of winter. Or, even better, on a clear summer day with a glass of cold beer to hand. But the point about Araucaria, or John Graham, who celebrates his 90th birthday today, is that it doesn't really matter. Tackling one of his crosswords is like having a teasing, gossipy conversation with an old and much-loved friend. You know it won't always be easy to follow, but it will always be worth it. He may baffle you but he will never cheat you. And when you've finished, you have a sense of satisfaction few compilers can offer.

He is immensely popular. Once I attended, and once I chaired, a session at which he talked about his work. On both occasions, a random member of the audience rose unbidden to thank him for all the pleasure he had brought. And it's not a generation thing; yes, he knows about Latin literature, and Shakespeare, and Dickens, but he also refers to popular culture of today, sometimes to the bafflement of solvers far younger than himself. And he needs all those sources: the size of his output remains astonishing. Six cryptics per month for the Guardian (plus more quick crosswords), some for the FT, two a month for 1 Across, the puzzle magazine he helped found, plus bespoke crosswords to celebrate people's anniversaries and special occasions. Like a tiny artist's studio, his study in the cottage where he lives near Huntingdon, Cambridgeshire, is festooned with works in progress.

It's not just the playful wit that delights the fans. He is also astoundingly inventive, as the special double holiday crosswords in this paper demonstrate. A crossword based on famous novelists? Or heroes of the South African liberation struggle? (John remains leftwing, and will never work for a Murdoch paper.) He invented the alphabetical crossword: clues for every letter of the alphabet, to be slotted in where by cunning deduction. Or the perimetrical: a long clue gives a 28-letter quote that goes around the edge. As he himself says, you have to have a certain type of mind to create such a thing. But not to solve it: once you have acquired the knack, you can generally manage. He has given his name – Araucaria is the Latin name for the monkey-puzzle tree – to his own style, Araucarian, which contrasts with Ximenean, after Ximenes (DS Macnutt, the Observer compiler who laid down regulations for the modern puzzle). It is looser, less rule-bound. For example, Ximenes would never have allowed John's favourite clue by another compiler (the late Bunthorne, also a Guardian favourite and a devout Araucarian): "Amundsen's forwarding address (4)" to which the answer is MUSH.

John was a churchman most of his life, but had to leave when he and his first wife divorced. After the loss of his stipend, crossword compiling was his only source of income, which is one reason he is so prolific. Most of us would be incredibly grateful to be compos mentis at all at 90; to be the purveyor of so much pleasure to so many people must be a wondrous feeling.